Deglaciation of the north American ice sheet complex in calendar years based on a comprehensive database of chronological data: NADI-1
Bibliographic record
Abstract
The most recent deglaciation of the North American Ice Sheet Complex (NAISC: comprising the Innuitian, Cordilleran, and Laurentide ice sheets) offers a broad perspective from which to analyze the timing and rate of ice retreat, deglacial sea-level rise, and abrupt climate change events. Previous efforts to portray the retreat of the NAISC have been focused largely on minimum-limiting radiocarbon ages and ice margin location(s) tied to deglacial landforms that were not, for the most part, chronologically constrained. Here, we present the first version of North American Deglaciation Isochrones (NADI-1) spanning 25 to 1 ka in calendar years before present. Key new features of this work are (i) the incorporation of cosmogenic nuclide data, which offer a direct constraint on the timing of ice recession; (ii) presentation of all data and time-steps in calendar years; (iii) optimal, minimum, and maximum ice extents for each time-step that are designed to capture uncertainties in the ice margin position, and; (iv) extensive documentation and justification for the placement of each ice margin. Our data compilation includes 2229 measurements of 10Be, 459 measurements of 26Al and 35 measurements of 36Cl from a variety of settings, including boulders, bedrock surfaces, cobbles, pebbles, and sediments. We also updated a previous radiocarbon dataset (n = 4947), assembled luminescence ages (n = 397) and gathered uranium-series data (n = 2). After scrutiny of the geochronological dataset, we consider >90% of data to be reliable or likely reliable. Key findings include (i) a highly asynchronous maximum glacial extent in North America, occurring as early as 27 ka to as late as 17 ka, within and between ice sheets. In most marine realms, extension of the ice margin to the continental shelf break at 25 ka is somewhat speculative because it is based on undated and spatially scattered ice stream and geomorphic evidence; (ii) detachment of the Laurentide and Cordilleran ice sheets took place gradually via southerly and northerly ‘unzipping’ of the ice masses, starting at 17.5 ka and ending around 14 ka; (iii) the final deglaciation of Hudson Bay began at 8.5 ka, with the collapse completed by 8 ka. The maximum extent of ice during the last glaciation occurred at 22 ka and covered 15,470,000 km2. All North American ice sheets merged at 22 ka for the first time in the Quaternary. The highly asynchronous Last Glacial Maximum in North America means that our isochrones (starting at 25 ka) capture ice advance across some areas, which is based on limited evidence and is therefore somewhat speculative. In the Supplementary Data, the complete NADI-1 chronology is available in PDF, GIF and shapefile format, together with additional visualizations and spreadsheets of geochronological data. The NADI-1 shapefiles are also available at https://doi.org/10.5281/zenodo.8161764.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.004 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".